My group's ranger picked up the Unearthed Arcana for the Ranger class but I have felt it to be weak and have since investigated the document.
Your animal companion has abilities and game statistics determined in
part by your level. Your companion uses your proficiency bonus rather
than its own. In addition to the areas where it normally uses its
proficiency bonus, an animal companion also adds its proficiency bonus
to its AC and to its damage rolls.
Our ranger picked a Wolf at level 3, and is currently level 6.
The Wolf's normal stats in the PHB say:
Prof. Bonus +2
HP 11 (2d8+2)
Bite: Melee weapon attack, +4 to hit, 5ft reach, one target. Hit 7(2d4+2) piercing damage.
If the ranger is level 6 and has a +3 prof bonus, the new stats should look like this in my opinion.
AC 16 (+3)
HP 29 (5d8+2)
Bite: Melee weapon attack, +5 (changing the +2 to a +3 yields +5) to hit, 5ft reach, one target. Hit 10(2d4+5) piercing damage.
Does this look right?